Foam plastic material is used to an ever-increasing extent in many areas such as containers, graphics art applications and the production of patterns for casting metal structures. It is often desirable to mould the images in relief on the foam, for example on cups, but the production of such images in a mould is costly and requires long runs to be economically viable.
It has previously been proposed in U.S. Pat. No. 4,578,329 to use a laser to mark a foam by "burning" an image on the foam. However, this arrangement requires the laser and/or object to be moved with a great deal of accuracy to reproduce the desired image and therefore complex images are difficult to produce.
Other proposals, such as that shown in U.S. Pat. No. 4,139,409, have utilized a mask to reflect the laser radiation. However, masks are difficult to manufacture and also difficult to apply to curved articles.